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Evolutionary divergence in the feeding mechanism of fishes

Wilga C.

Acta Geologica Polonica

2008

Vol. 58, no. 2

113-120

After the divergence of chondrichthyans and teleostomes, the structure of the feeding apparatus also diverged. Hyoid morphology varies considerably among fossil and extant elasmobranchs and has been hypothesized to be related to feeding style. How hyomandibular morphology affects function during feeding is of great interest since hyoid movement is a key component in the feeding mechanism. Cranial kinematics and buccal pressure during feeding was quantified in elasmobranchs and teleostomes. The feeding mechanism in elasmobranchs with anterior (AHY) or lateral (LHY) directed hyomandibulae differs from teleostomes primarily in hyoid movements due to morphological constraints. The hyoid expands ventrally during feeding in the species studied; however, the hyoid laterally compresses in AHY and LHY species but not in teleostomes or shark species with posterior directed hyomandibulae (PHY). Anterior and lateral hyomandibular orientation in elasmobranchs constrains them to adduct during feeding. This represents a fundamental difference in the feeding mechanism regardless of feeding style between elasmobranchs with AHY or LHY compared to sharks with PHY and teleostomes as a result of morphological divergence in hyoid morphology. It appears that posterior directed hyomandibulae may have evolved to increase the gape in specialized bite feeding sharks while lateral directed hyomandibulae evolved in specialized suction feeders.

Late Cretaceous sharks in the Opole Silesia region (SW Poland)

Niedźwiedzki R., Kalina M.

Geologia Sudetica

2003

Vol. 35

13-24

The upper Cretaceous deposits of the Opole Trough contain rare but relatively diverse shark teeth, mainly from ptychodontid sharks (Ptychodus latissimus Agassiz, 1843, Ptychodus polygyrus Agassiz, 1843 and Ptychodus mammillaris Agassiz, 1843), Anacoracidae (Squalicorax sp.), Mitsukurinidae (Scapanorhynchus raphiodon (Agassiz, 1843)), Alopiidae (Paranomotodon angustidens (Reuss 1845)) and Cretoxyrhinidae. Paranomotodon angustidens has not previously been reported from the Opole Trough. The selachians from the Opole Basin can be divided into two trophic groups: bottom-dwelling ptychodontid sharks with a diet consisting of shelly invertebrates, and pelagic Lamniformes, which were active predators feeding on fast-swimming fish and reptiles. The morphology of the teeth, signs of abrasion and the analysis of the invertebrate assemblage from the Opole Cretaceous suggest that the ptychodontids fed on inoceramid bivalves, while the lamniform sharks fed mostly on fish. Lamniformes live in all marine environments, and their remains are numerous in all the lithostratigraphic units of the Upper Cretaceous in the Opole Trough. The teeth of deep-water ptychodontid sharks are only abundant in the middle part of the Middle Turonian sediments. Nearshore shark remains are extremely rare in the Cretaceous deposits of the Opole Trough. This indicates that the Middle Turonian (middle I. lamarcki Zone) represents the deepest environment of the Opole Cenomanian and Turonian .